Up-down asymmetry of neutral current events as a diagnostic for νμ−νst versus νμ−ντ oscillations

We show that the asymmetry in the neutral current events (e.g. νN→νNπ0) can be used to discriminate between νμ−ντ and νμ−νst mixing as being responsible for the atmospheric neutrino anomaly. Specifically, AN vanishes for νμ−ντ mixing and is about 2/3Aμ for νμ−νst mixing. We also comment on the possibility of mixing of all three neutrinos (i.e. νμ−ντ−νst) which can give a muon asymmetry as large as 1/2.